1. Field of the Invention
The present invention is directed generally to a rotor system for a helicopter. More particularly, the present invention is directed to a rotor system having elastomeric flap and lead-lag bearings and a curved, continuous loop twin composite tension/torsion beam. The rotor system is also distinguished in that pitch bearings are eliminated.
2. Prior Art
The blade mounting and support system in a rotary blade aircraft such as a helicopter is conventionally a very complex and complicated mechanism. For example, in the fully articulated rotor blade, the blade is required to move in several different but related paths during its operation and a separate bearing assembly has been required for each motion. The blades flap about a horizontal axis with respect to the rotor blade to either cone or droop. They also twist or rotate about their own longitudinal axis as the blade pitch is changed. Additionally, the flapping and air drag caused as the blade rotates result in blade lead or lag motions wherein the blade moves slightly in the horizontal plane about a vertical axis at the blade attachment.
In prior art blade mounting and attachment schemes, a number of lubricated bearings have been required to provide for movement of the blade through the various motions it must perform. Lead/lag bearings, flap bearings, pitch bearings, and fixed end torsion/tension straps have been conventionally used to mount the blade to the rotor. Each of these bearings requiring lubrication has a lubricating oil reservoir and flow lines associated with it. As the helicopter operates, these bearings wear, seals leak, the oil reservoirs need to be replenished, lines clog, and other problems arise. The maintenance of such a system is a time consuming and tedious chore which must be performed at relatively frequent intervals to ensure safe operation.
In many of the prior rotor systems heavy steel and aluminum forgings for housing the above described lubricated roller or ball bearings are used. The overall size of the rotor hub system is affected by the size requirements of these bearings and lubricant reservoirs thus adding to the hub cross-sectional area and parasite drag. The more parasite drag, the more power which is required to overcome it and the less power available to move the aircraft.
The tension/torsion member in the prior art devices may be made of laminates of steel which permit torsion flexure while carrying centrifugal force from the blade attachment housing to the rotor hub. Again, this structure has added weight, size and drag to permit as great a degree of blade pitch motion as is desirable. The tension/torsion member connection points are subjected to high stress and require periodic inspection.
Thus, the prior art rotor hub and blade mounting assemblies are complex and heavy and require frequent maintenance, and inspection and have a large amount of parasite drag.